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advantageously applied through their instrumentality. I hope the ENGLISH MECHANIC life-boat fund will be a success, and that you will secure a good attendance at your forthcoming concert. RICHARD LEWIS.

THE LUNAR CRATER PLUTO. SIB.-The results of observation of the floor of the lunar crater Pluto which have appeared elsewhere see Student, April, 1870, p. 161 being of interest in connection with questions now agitated relative to changes on the moon's surface, the following summary of further observations during the April lunation may not be uninteresting to your numerous readers.

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IRON STRAP

WITH EXTRACTING CHANK

FIG. 2

E.

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The observations were made by Mr. Gledhill; of Mr. Crossley's Observatory, Halifax; Mr. Pratt, of Brighton, and Mr. Elger, of Bedford. Sixteen only of the 35 known spots were seer; they are numbered 1, 3, 4, 5. 6, 9, 11, 14, 16, 17, 22, 24, 25, 30, 32, and 33, but Mr. Gledhill detected an unrecorded one, which is numbered 35. Of these the following were seen by the three observers-viz., Nos. 1, 3, 4, 5, 16, and 17; no doubts, therefore, can be cast on their visibility during April. No. 14 was observed by Messrs. Elger and Pratt on seven occasions, but missed by Mr. Gledhill. The spots seen by Mr. Gledhill only were Nos. 6, 9, 11, 30, 32, 33 and 35; by Mr. Elger only, Nos. 24 and 25, and by Mr. Pratt only, No. 22. Taking spot No. 1 (the most constantly seen) as the standard 100, the degrees of visibility are as under:Spot 1 4 3 17 5 16 14 9 25 Vis. 1000 1000 895 789 471 421 368 263 263 Spot So 6 11 24 22 32 33 35 Vis. 210 •105 105 105 053 053 053 053 The number of cbservations of the spots between position to be efficiently used for hauling off the life direction required, and, finally, the double rope be in April, 1869, and March, 1870, inclusive, amounted to boat. Fig. 2 shows a sketch of the position of the 771 in 108 series; those during April amounted to 118 "Otter" floating, seen from above. A B shore line. in 19 series. These numbers give 7 for the average numLE trailing line, by pulling which the upper frame is ber of spots visible on any one evening. The curves of drawn away. K I double rope to shore. The machine visibility of 14 spots have been projected for the 12 lunato be fitted on a small carriage with long pole and tions ending March, 1870, and of these 14 spots 5 were launching ropes, as in life boat carriages. Two not seen on any one of the 19 sets of observations-wheels only are wanted for carriage. The whole viz., Nos. 2, 7, 10, 13, and 19. affair might weigh from 4cwt. to 6cwt., including carriage. SUFFOLK AMATEUR. P.S.-I may just add an idea about self-righting The principle is as old at least as any his play boat, and deduced from the observation that grown man who, as a small boy, put a leaden keel to the form of the upper works has nothing to do with the matter, but that it depends altogether upon the centre of gravity or otherwise on weight below overbalancing weight above.

The intermittent character of the above unrecorded spots in April is becoming more and more manifest. No. 2 has been observed 7 times only between August, 1869, and March, 1870, inclusive. No. 7 invisible in June and July 1869, and in February, March and April, 1870. No. 10 invisible between Oct, 1869, and January, 1870, inclusive. No. 13 seen on 28 occasions during the past year, invisible in April, 1870. The same may be said of No. 19, it having been seen 27 times during the last year, and invisible in April, 1870. No. 22 may be included in the same class, for although it was recorded on every fine evening in August and September, 1869, it is now but rarely seen. The variations in the visibility of the spots more constantly seen lead to the same conclusion-viz., that their visibility is also intermittent. It must, however, be borne in mind that the visibility of spots very rarely seen, once or twice for example, in the course of a lunation, may depend upon the state of the earth's atmosphere; it is, nevertheless, difficult to conceive that the earth's atmosphere is capable of obscuring spots for months together, while others quite as difficult of perception are visible.

An increased accuracy is attainable by the number of observers being augmented, for, as in all observations of the kind, errors that necessarily affect the few are eliminated in the case of the greater number, so errors arising in the visibility of the spots from differences in the state of the earth's atmosphere at distant stations, and also in consequence of the overlooking of minute objects by one observer which are distinctly visible to another, disappear to a great extent, when the observers are numerous, the greater weight being accorded to the visibility of those spots that are seen by the greatest number of observers.

W. R. BIRT, Cynthia Villa, Walthamstow.

life boats.

FAIRY WHEELS.

SIR,-1 enclose you the only one I have left of these ancient stone dises, trusting you, or some of your correspondents, may be able to throw some light as to the purpose for which so much trouble has been bestowed on them; they are only found in one field on the farm, but were much more plentiful forty years ago than now; at that time, we used to suppose they had been made by children, as wheels for toy carts. One of my ploughboys, about this time last year, picked up about a dozen of them; he brought four or five home, throwing the others away. The one I forward is much the smallest, and the thickest. I am sorry to say the others are all lost; the one I send is much more carefully made than any of the others were. None of them were the same size or thickness; some of them showed the saw marks very distinctly; they had been sawn out of cylinders of different sizes; the

The

Liebig's process as given by Browning, this being the
only process I have attempted. The proper cleansing
of the glass is doubtless equally as necessary in both
processes. In the first place, distilled water, that is,
chemically pure, must be used, I have not tried rain
water, but should think it would succeed when col-
lected in clean vessels and properly subsided. 2nd.
The chemicals should be obtained of a reliable chemist
nitrate of silver is, I believe, ordinarily good.
potash must be pure by alcohol. The ammonia should
be the strongest obtainable. In cleaning the glass, the
strongest nitric acid should be used; if good it gives
out copious fumes, and may be easily known by the
prompt manner in which it attacks the eyes and nose.
First place the mirror face upwards (previously
cemented to the wooden block) in a large dish, pour
the nitric acid on it, and gently rub the glass all over
its surface and sides with a pad of medicated wool
plugged into a glass tube; then rinse the wool in com-
mon water, and repeatedly wash off the excess of acid,
taking care to give the same attention to the sides as
to the surface; this done, do not touch the glass with
the fingers, but take hold of the block to which it is
attached, and hold it under running water from a tap for
about five minutes, continually moving it, that the jet
may play freely over the back, the sides, and lastly the
surface; then examine the surface of the glass, and if
the water has a tendency to run away from the edge of
the disc, as if greasy, the process must be repated un-
til all greasiness disappears. The glass is then laid
in a sloping position, and another woollen brush used
to cleanse it with distilled water; this brush should not
be touched with anything but distilled water, into
which it is now dipped, and the glass repeatedly rinsed
all over with it, until any apparent greasiness which
entirely disappears.
the first contact with distilled water may occasion

The glass is now ready for silvering, and is laid wet, face downwards, in a dish containing a little pure alcohol (just sufficient to touch the entire face of the glass) until the silvering bath is quite ready. Caution must be observed throughout the entire process not to touch the face of the glass once with the fingers if possible. One or two particulars as to the silvering fluid may be serviceable. If the process is conducted in cold weather, it is advisable to warm the solution slightly; this may be done when the distilled water is added, by warming some of it in a clean cup placed in subside the precipitate more quickly, and renders the a basin of hot water for a few minutes; this helps to fluid transparent before pouring into the silvering dish, which is necessary to prevent spots in the silver film. Another essential item is to completely dissolve the milk sugar; this can scarcely be done in cold water, but is quickly done by warming in a cup placed in hot water, as before. The slight warmth given to the silvering fluid has also the important advantage of giving a harder and more adhesive film.

care should be taken to enclose no bubbles under its In placing the mirror face downwards in the bath, surface; one side should be lowered first, and then the entire surface brought gradually level; it should not sink too deep into the fluid; the nearer the surface the better, providing the face is fairly immersed. When the film is complete, it is removed and immediately washed under the tap for five minutes as before, then stand the mirror on edge in a dish, and gently rinse with distilled water either with the woollen brush or with a piece of soft clean sponge; when it is thoroughly dry, polish first with clean wash leather, then with rouged leather.

of a diagonal plane for a Newtonian may be estimated In answer to Mr. Gray's query, the proper aperture

1

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its size, providing the focus of speculum is thrown just outside the great tube, as is usual.

As the "Harmonious Blacksmith" and "F.R.A.S." have associated my name with the subject of "platinised mirrors," I must admit my entire ignorance of the process, and as to the advantage of platina over silver in point of reflecting power, I should have serious doubts, and as to the "baking process" for such sensitive things as specula I should have very little doubt, and should require positive evidence to convince me that it could be anything else than a failure. W. PURKISS, 9, Cumberland-street, Roman-road, N.

"OTTER" FOR LIFE BOAT SERVICE. SIR,-Amongst the requirements for life boat service, it has been held to be a desideratum to find means for depositing an anchor on emergencies at a distance from the shore convenient for using a block and double rope attached thereto, to enable those on shore to haul off a boat through surf, and to the various schemes for this purpose, I wish to offer an additional one. There is a certain fishing implement of the pot hunting or poaching class, by which a line can be carried out (with hooks, &c.) called an "Otter," the construction and action being this: A flat board holes through have been bored after each disc was cut is (by being weighted with lead) made to swim edge-off, some of them quite oblique, but all rimmed from each side as this is; they were all thick in the middle, of this, neither had any of them the perfectly flat side you see in this one. I do not know of any stone in this neighbourhood that at all resembles this they edges, as though the notches had been cut with a file; are made of. I recollect seeing them with serrated I also believe I saw some of the same dug up at Uriconium (Uttoxeter), about two miles from here. drilled through them, I should say it has been for the From the careless manner with which the holes were purpose of threading them on a string; the one I send has evidently lain in the ground very many years, by the gravel being so firmly attached to it. The opinion of some of your readers on it will oblige. I have seen some quite twice as large, and above

ways; to it is attached a loop similar to the bellyband though none were so much rounded off as the one side drill for boring purposes, by means of which a cham

of a boy's kite; to the loop is fastened the fishing line in a certain position upon launching and paying out the line. The "Otter" leaves the shore in an oblique direction, and is hauled along to the extent of the line. On this principle it is proposed to construct a machine of the following description. Fig. 1, A BO is an anchor, of which the ring is at A, and single fluke BO attached to a flat frame built up of board and cork, A BDC, the upper portion of which, C E FL, is removeable, sliding out from the lower portion backwards, having line and ring fastened to it L E, the whole of such buoyancy as to float the entire machine level at about the line EF, G K H loop or belly band, to which, in proper position for effecting the oblique motion in hauling off, are fastened a block and double line rove there through I K. A stronger connection is to be made between the block K and anchor ring A, by line or rope A K. In use, the upper sliding portion of the frame is to be fastened by a line 3rd the strength of the line L E, also the bellyband is to be so contrived that the sliding out of the upper part of the frame shall let it fall loose. The action is presumed to be this (i.e., supposing this salt water "otter" behaves equally well with its fresh water progenitor, and there seems no reason to suppose it otherwise), that upon launching, the machine drawn by double rope KI, will proceed to sea, and gain offing according to length of rope K I, trailing behind it the line L E. On acquiring proper offing and position, the travelling line is to be jerked so as to break the fastening 3rd its strength, and pull out the upper sliding portion of the frame, which is to be hauled ashore, and also

half as thick.

A SUBSCRIBER.

SILVERING SPECULA.

SIR, Although I am no chemist, and am therefore unprepared to account for some of the failures which may happen in the above art, my own repeated failures have, nevertheless, taught me a few lessons, and have led me to the opinion that nine cases out of ten of these failures occur chiefly through want of sufficient care in cleaning the glass surface intended to be silvered; and although the few hints I have to offer do not perhaps apply entire to the " Rochelle salt" process, your correspondents, M. Gray, p. 163, and " Interested." p. 191, may, I hope, find them useful as regards the washing.

The following particulars as to chemicals refer to

EXPANDING DRILLS FOR MINING PURPOSES. SIR,-In the issue of the ENGLISH MECHANIC of the 6th inst., I find you have inserted a short paragraph (taken from the Mining Journal) relating to an invention by Mr. E. P. Gleason, of an expanding ber or cavity can be made at the bottom of a drilled hole, for the reception of the blasting powder, and by which means a vast additional force can be obtained for disintegrating and blowing up the rock. Now, it so happens that I myself invented a similar drill borer about seven years ago, a description of which, at the time, appeared in the North Wales Chronicle, which was extracted the next week after its appearance in the columns of the Mining Journal. Judging from it in the note in question, it would appear that similar in principle, and pretty nearly so in the carryMr. Gleason's invention and my own are precisely ing out of it in detail, which certainly is a somewhat part is composed of two cast steel blades, which are strange coincidence. In my invention, the cutting inserted about 4in. above the bottom of the frou rod, the blades being screwed in so as to be the more easily taken out or replaced when they require sharpening. The chamber at the bottom, has à diameter of 3in. (the hole made by the common borer being 14in. in diam.), and as the perpendicular hole is continued by the operation 4in. or 5in. below the chamber, the latter can be extended to any reasonable depth. My expanding drill-borer has been successfully tested in several slate quarries in the neighbourhood, and notably so at the Hendre Ddu slate quarry, near this town. Sir Edward Poore was at that time the managing director of the said quarry, and was assisted by Mr. W. Jones, a thoroughly practical miner. experimented on a large piece of rock, and a hole was drilled to the depth of 11ft. The charge was 1016. of rock powder, and above 500 tons of rock were

We

JOHN WILLIAMS (Joan Madoc), shipsmith, Port
Madoc, Carnarvonshire,

P.S. How could I find the focal length of a small concave lens.

WATER ANALYSES.

blown up, the explosion being a tremendous one, and tool buried in the clean metal under it; but some cast-piece would have with any given O. G.? An example the rock was shattered in all directions. This resultings are so uncommonly hard that no tool will touch would greatly oblige. 5th. How are the webs in a was considered to be most satisfactory by all who them, especially those cast in the country, and it is imtransit eyepiece protected? 6th. What is the plan of were present and witnessed it, as the quantity of slate possible to do anything with them. If" Amateur the pancratic eyepiece? I have often heard of it, but rock obtained by the powder charge of 10lb. was Turner" will tell me the diameter of his work, I shall never saw one. 7th. Is Kepler's third law exact? Sth. equal to what was usually obtained in the quarry by be able to inform him how many revolutions the man- Would not" F.R.A.S." describe a spectroscope more the expenditure of 100lb., to say nothing of the great drel should make in one miuute to give the proper minutely than he did in No. 267? I am sure it would be expense saved in the matter of labour. From this cutting speed. interesting to a great many of us, especially now as be you will perceive that Mr. Gleason's invention has As to the second part of the question; a cylinder is going to tell us something of its uses. 9th. What is been long since anticipated by myself, in an obscure may be bored very fairly by setting it up on the face- the size of the Cambridge (U.S.) refractor, and also town in North Wales. As a contributor to your valu- plate of the lathe, if a large one (a small one may be the Melbourne Telescope? SCORPIO. able paper for the last four years, I trust you will do soldered on to a brass chuck or held in the cup chuck) me the justice to admit this letter in the next number by one flange, and running an inside tool through it of the ENGLISH MECHANIC. by means of the upper slide of the rest, taking care to get the slide set perfectly parallel to the axis of the mandrel, and frequent use of the callipers is the only means of ascertaining this. But there is another plan which I think is superior to the above (if " Amateur Turner" is the happy possessor of a screw cutting lathe), and that is to set up the cylinder to be bored on the saddle of the slide rest (the rest itself removed) and fixing a cutter bar with projecting cutter between the centres of the lathe and causing it (the cutter) to traverse through the cylinder by the sliding of the saddle; this, if properly managed cannot fail to produce a truly cylindrical bore. Cylinder covers are turned by chucking them in a wood chuck, and turning one side and edge, then reverse them to turn the other stde. And now, having answered the above questions, allow me to ask one of my fellow-readers-viz., What is the construction of Hoitzapffel's screw cutting tool-holder or cutter bar for V or square threads, by which the tool may be adjusted to the exact rake of the thread. A drawing to scale would oblige. G. W. A.

"C. R. O., HANTS," ON SEVERAL MATTERS. SIR," Salopian," on page 190, wishes to know how it is that the circumference of the earth at the Equator is greater than the circumference drawn through the poles; he quotes the difference at 25 miles. A moment's reflection will show him what a mere trifle this is when we take into consideration the vast dimensions of our globe; I question very much if many billiard balls-perfect as they apparently arecan boast such a slight departure from the form of a true sphere. I believe myself that centrifugal force certainly causes what "Salopian" refers to, and that its power, exerted throughout the whole mass of the revolving earth, is just so much, and no more than sufficient to occasion this swelling out at the Equator. This opinion will, I think, in no way stultify the arguments in my previous letter on the earth's rotation.

Touching this same subject, I must confess that it was with the greatest possible gratification I read Mr. Proctor's kindly-worded comment on my letter; encouragement from that gentleman is worth something. Will he allow me, in my turn, to present my compliments to him, and trust we may often have the pleasure of reading his most valuable contributions to our MECHANIC?

An apology is due to "An Adept," inasmuch that I have delayed so long acknowledging his kindness in replying to my question on the construction of Bourdon pipes. The fact is, I have been waiting, unwilling to bother him during his unfortunately still continued indisposition, but seeing that other correspondents are not so considerate, and fearing that he may perhaps deem me ungrateful, which I assure him is very far from the case, I can hold out no longer. The plan that gentleman suggested-viz., to place the pipes in two rows, would have been obvious to me, had the special circumstances of my case admitted of it; I worded my letter badly, and "An Adept " naturally thinks depth is no object. What I wish to ascertain is, could a pretty good quality of tone be obtained from pipes constructed with a much greater depth than usual in proportion to their width? For instance, could CCC be made 44in. by 8in. internal measurement? The double row plan I wish to avoid if possible, for many reasons. I trust our correspondent may soon be restored to perfect health. What in the name of all that is polite and charitable,

COLOUR BLINDNESS AND ASTRONOMICAL
OBSERVATION.

SIR. With reference to the letter signed "W. R." in your issue for May 13, page 187, there are or rather were four modes of estimating the organic matter in water Firstly, the original old method of treating the solid residue obtained by evaporating the water to dryness, and estimating the loss, which was ascribed to" organic matter." This is now quite abandoned as being unsatisfactory and altogether erroneous. Secondly, there is the system of estimating the "organic matter" by means of an acid solution of permanganate of potash, as detailed by Prof. Miller in his paper entitled "Observations on Some Points in the Analyses of Potable Waters," in the "Journal of the Chemical Society," 1865, Vol. XVIII. This, however, has been proved to be quite unreliable, besides being unsatisfactory at the best. In fact, Prof. Frankland's comment on it, "totally untrustworthy," has been thoroughly well sustained by succeeding trials

with it.

The third system is that of Messrs. Wanklyn, Chapman and Miles Smith, and is detailed at length in their SIR,-The readers of the ENGLISH MECHANIC have Society on the 20th of June, 1867. This system which paper on Water Analyses," read before the Chemical recently been entertained with a rather acrimonious discussion on the subject of the colour of the belts of was criticised by Mr. Dugald Campbell (" Laboratory," Jupiter by two of its most valued contributors. Vol. I..) and again verified and slightly amended by Prof. Wanklyn in his " Verification of Messrs, Wankone of the letters I perceive that one of the disputants lyn, Chapman and Smith's Method of Water Analyses" admits that an eye "successful in detecting minute in the Journal of the Chemical Society," new series, Vol forms of detail may altogether fail to notice grada-V., p. 591, disputes with Professor Frankland's method the claim for pre-eminence.

tions of colour."

Ju

This fact has been considerably enlarged upon by
"Omicron in the series of articles on Colour-blind-
ness, and it appears to me that there is clear evidence
in the columus of the MECHANIC of a case of colour-
blindness, although there is not, perhaps, sufficient
evidence to determine which one of your correspon-
dents is affected with abnormal vision.

Mr. Browning says of the drawing of Jupiter that
appeared in the Student that "the yellow and red are
too bright, and the ashy blue or gray far too dark."
Mr. Denning says that the colour of Jupiter, as seen
in his telescope, was very apparent, but not so dark as
shown in the print. Mr. Grover says that the colours
in the drawing are certainly too vivid.
to these remarks, Mr. Purkiss holds the opinion that
In opposition
Jupiter appeared even more vivid than the engraving
in the Student. Perhaps these conflicting remarks are
hardly sufficient to warrant the charge of colour-
blindness, as "Omicron" has employed the expres-

sion, for the discrepancy in the description is one
rather of quantity than quality. But as the term
appears to be applied to every degree of deficiency of
appreciation of colour, I have adopted it here.

It

The fourth system is that of " Frankland and Armstrong," the principle of which is detailed by Mr. Davis on page 87 of the ENGLISH MECHANIC. This organic nitrogen and carbon, and theoretically is system is based on a gasometric estimation of the the finest and most accurate of the four. Professor Frankland's paper in the "Journal of the Chemical Society" violently attacks the method of Messrs. Wanklyn, Chapman and Smith, and in it the author attempts to demonstrate the thorough unreliability of their system by means of a systematic series of analyses, comparing the results obtained by his use of Messrs. Wanklyn's, &c., method, with the reputting down the former as wrong on account of the sults furnished by his and Armstrong's process, and difference between the former and the latter, which is assumed to be correct.

the Chemical Society," Vol. XX., attempts to prove the

Prof. Wanklyn retaliated, and in the "Journal of unreliable character in practice of Frankland and Armstrong's method of gasometric analysis, and vigorously defends his own system. He also shows by reference to Mr. Miles Smith's paper in the "Laboratory," Vol. I., p. 114, the danger and liability to error of any result based on the analyses of the residue obtained by evaporating to dryness a large quantity of water. Since then the discussion and rivalry between the two and Chapman having improved their position by their methods has waxed hot, Professors Wanklyn, Schenk,

can "Eleve"-himself, I presume, a musical manmean by putting such a questiou as this to your correspondents? Tell me why a double manual instrument should be preferred to a single, if the single set Since three observers are inclined to one opinion. of keys can be made to do the work as well?" Is this and one only holds the contrary, I should be inclined from Lord Dundreary, or what? One might just as to suspect some anomalous vision to have vitiated Mr. sensibly put the query, why eat bread and butter when Purkiss's observation; and the object of the present bread alone could probably do its work just as well in communication is to ask your readers whether an nourishing the animal system? Amateurs, and intend- abnormal vision, manifested in any considerable ing purchasers, make no mistake, you will get incal- degree, as in some of the cases specified by " Omicron," culably more real and lasting satisfaction from a would be likely to produce telescopes in which chro-masterly analysis of the "Action of Limited Oxydisadouble manual than a single; ask any organist, matic aberration would not be duly corrected. tion on Nitro and Nitrogenous Organic Bodies," and Chorus and fugue playing may be performed very well of the action of alkaline permanganate of potass on appears to me that if the correction can be computed organic bodies. Professor Frankland in turn has imon a single manual, but how about" He was despised," by mathematical formule, it is not likely to produce proved the reliability of his system by Mr. Herbert from the "Messiah," or, "O, rest in the Lord," from any ill effect; but if the correction be determined by "Elijah," and the hundred and one other pieces continued examination of the image of an object, and Gas Analysis," in the September number of the McLeod's papers On a New Form of Apparatus for depending for their very life and soul on a clear, dis- continual grinding, till the object is seen to the satistinct, and individual melody? To my mind the har-faction of the observer, depending upon no fixed law, ratus for Determining the Quantities of Gases Exist"Journal of the Chemical Society," 1869, and "Appamonium, especially, requires two manuals, from the ing in Solution in Natural Waters." in the "Journal very nature of its tone, whose most marked characteristics are, in a good instrument, an apt capability of the Chemical Society," Vol. VII., new series; and for producing grand and majestic harmonies, but there Dr. Russell's paper read before the British Association, always seems to be a falling off when anything of a melodic character is attempted, hence the value of two rows of keys. I on my side appeal to the "Harmonious Blacksmith" for his verdict; his writings, which every one must enjoy, speak well for the value of any opinion he may offer.

The subject of harmoniums naturally associates itself with Mr. Hermann Smith, and if you, Sir, have been instrumental in bringing him back among us, you have my most cordial thanks. Let any one peruse Mr. Smith's chapters on the harmonium, from their commencement, and see what ground he has broken up, before untrodden, and what vistas of thought, apart from the mere dry details of construction, he has opened out to a thinking mind. A pains taking and conscientious writer, Sir, and a comrade

we cannot afford to lose from our ranks,

I am delighted to see such a long list of extracts from various correspondents relative to the success of our paper. You merit our very warmest praise and congratulation. There can be no doubt that to your own able and talented leadership all the increasing excellence of this periodical is due; you have indeed reason to be proud, Sir, of your achievement, for the press has certainly never before sent, through the length and breadth of the land, such a mass of useful lieterature at such a nominal price-no, nor at any price. My best wishes are yours. C. R. O.

TURNING.-BORING CYLINDERS. SIR.-On page 189, Query 3701, a question is asked relative to turning, which, with your permission, I will answer.

I imagine the cause of "Amateur Turner's "failure is the speed at which he drives his work, as no tool will stand, even against soft wood, if it is driven at too great a rate. The best way that I find to take the Scale off cast iron is take a moderately deep cut at first, Bo as to get underneath the scale, and the point of the

but left to the option of the observer, the question is
one of some importance.

1869.

It is needless for me to say that I am ignorant of the
method employed by makers for correcting the chro-
matic aberration of telescopes; and if it is not asking
Mr. Purkiss to reveal the secrets of his guild, I should lutely the best. With our present knowledge, per-
It is at present difficult to determine which is abso-
be glad if he would give me some information, espe-haps, theoretically Frankland's is the most accurate,
cially as regards refractors.

COLUMBUS.

but a systematic research may at any time turn the tables, and leave Wanklyn's the best, while chemists are undecided, many taking each side, while others, the majority, take neither.

Neither the alkaline perinanganate process of Prof. Wanklyn and his colleague at the London Institution; Royal College of Chemistry, however, are perfect, nor the gasometric system of Prof. Frankland, and the and, strange as it may seem, neither of them are capable of correctly and accurately estimating the actual amount of the nitrogenous organic matter, as Dr. Phipson and Mr. Paul remark. It is true Dr. Fraukland, in his article in Vol. XX., page 72, of the "Journal of the Chemical Society," goes so far as to deny its practibility at present, but that is too sweeping a conclusion.

detailed

THE TELESCOPE. SIR,--Many thanks to "F.R.A.S," for his kind answers to my last queries. The reason I asked would he think testimonials to Solomon's £5 telescope, the following a 3in. telescope good, was because I saw among the from the Rev. F. E. Winslow, In Mr. Proctor's book on the Telescope. I find the following passage about the trapezium. The trapezium affords a useful test for the light-gathering power of the telescope. Large instruments exhibit nine stars; but our observer may be well satisfied with his instrument and his eyesight if he can see five with 34-inch aperture: a good 3in. glass shows four distinctly, but with smaller apertures only three are visible, and in a note he adds, I have never been able to see more than four with 3in. aper- used in connection with the Royal College of Chemistry At present, therefore, Professor Frankland's system ture.' Now with the telescope I obtained from you apparatus, as last year, I can see five stars in the trapezium." All of in No. 81 the new Solomon's £5 telescopes are warranted to show five by experienced hands, is theoretically the best, and series of the Journal of the Chemical Society," and stars in the trapezium Oriouis. It was in page 34 of in practice ay yield the most accurate results. But, the current volume, that "F.R.A.S." said, in answer to on the other hand, it is long, difficult, and complicated, "A Poor Lad," "A 24in. object glass could not pos- utterly unreliable in inexperienced hands, and, from sibly divorce anything closer than a pair of stars 25 its very complication, liable to grave errors, which the apart;" however, “ F.R.A.S." may not have mount a number of reductions and calculatious afford every 6 mag. pair. And now, Sir, I must with your permis- chance of being increased to a serious extent in passing sion, trespass on "F.R.A.S.'s" kindness a little more. through these manipulations. These, in connection Would he be so kind as to answer the following with other matters, operate to such a degree as to queries:-1st. Where can I obtain the "Nautical Al-rez.der it possible that no two analyses of the same manac," and what is its price? 2nd. What moderately water will agree. cheap book gives the best list of R.A. and declinations? rd. Is there any essential difference in the mounting of reflectors and refractors? That is would it not do to take a del for a small refractor from an Equatoreal reflector. 4th. How can I caleulate the field of view that any given Huyghenian eye

Finally, therefore, in practice, Frankland and Armstrong's process is not to be depended on unless a long series is taken, and the average struck off; while its complication, difficulty, and length, together with the complex apparatus and many reductions and calculations, render it so liable to serious errors

as to

MAY 27, 1870.]

ENGLISH MECHANIC AND MIRROR OF SCIENCE.

quite outweigh the advantage it has of affording the total empirical formulæ of the organic substance. It also has the disadvantage of giving no easy standard of comparison with others, and of not in the slightest classifying the organic matter.

Messrs. Wanklyn, Chapman, and Smith's process is indisputably the shortest and easiest, and more. over is such as can readily be done by anyone. It enjoys the advantage of classifying direct the nitrates, nitrites, ammonia, urea, and albuminoidous and nitrogenous organic matter into separate classes. It is very little liable to error, and besides affording an easy standard of comparison, can always be depended on to afford an exact agreement in its result between waters of the same composition.

It has been alleged against it that with waters containing the same exact amount of nitrogenous organic matters, but of different constituents, it will yield different analyses, and that with waters of different quantities of oxydised and nitrogenous organic matter of different constitution it will yield similar results. This is true; to a slight extent it will, but the gasometric system does the same to a far greater extent. It has also been stated that Messrs. Wanklyn, Chapman, and Smith's, permanganate of potass process suffers under the objection of being liable in a certain degree to under-estimate the nitrogenous matter; this is also, to a certain extent, true, as it is indisputably possible for it to so happen, but it could only so occur with perfectly harmless compounds, not known to exist in water, and then to but a very small degree. Messrs. Frankland and Armstrong's gasometric system labours under the much more serious difficulty of being extremely liable to very considerably over-estimate the nitrogen, and of confounding the innoxious and the dangerous nitrogenous matters together. "W. R." will From the above, your correspondent gather that personally I am of opinion that at present, for general purposes, Messrs. Wanklyn, Chapman and Smith's permanganate process is the best, though for some purposes, Messrs. Frankland and Armstrong's gasometric system in preferable.

In reply to his queries, it is possible to use both Wanklyn and Frankland's process for sewage analyse, and, perhaps, for that course of analysis, it would be as well to estimate the total nitrogenous matter by Frankland's system, and confine Wanklyn's to free ammonia, urea, and albuminoids.

Nessler's test can satisfactorily be employed for estimating ammonia salts, and for small quantities is much better than standard acid.

Finally, it is practicable, but not advisable, to use Wanklyn's system for manures; neither should I recomURBAN. mend Frankland's.

EXTRACTS FROM CORRESPONDENCE.

says:

TESTED RECIPES.-"A Morayshire Man "I am of opinion, with a number of other correspondents, that those furnishing answers to queries for recipes should add whether they have been tried and proved, or, if they were extracted from some author, as the case may be. I am confident a number of these answers are not worththe space they occupy, and, consequently, a loss of time and money to many a one who tries them, both of which the person may be ill able to spare. And with a few consecutive failures, many a person may become disgusted with the recipes (never blaming himself of course), and if not the loss of a subscriber to the MECHANIC, at least the loss of a correspondent. I have found a number of these recipes useless. Not at all times so much the fault of the recipe itself, as to the manner of preparing it."

the whole draught of the rollers together) that he has
a draught of 12 instead of 7."

READINGS FROM THE GLOBES.-J. Dyer
states: In T. S. H.'s' letter, entitled Readings
from the Globes,' at page 208 of the ENGLISH
MECHANIC, the following statement is made: As
the globe turns on its axis from west to east, those
who live in west longitude must have their time
earlier than those living in east longitude, because
they will not come into the enlightened hemisphere
so soon.' The word earlier should be later. As the
sentence stands, the last part contradicts the first."
THE WANDSWORTH TELESCOPE.-E. Salter
to reside in this
says Having recently come
Wandsworth
remarks respecting the great
locality (Clapham Junction), and noticing Mr. Webb's
Late
Telescope, I have been induced to try to seek it out.
which it used to stand a gentleman named Stilwell, an
After two or three failures I met near the spot on
personal knowledge.
inhabitant of Wandsworth, who gave ine the following
Pointing out the enclosure within which the instru-
particulars from
ment was erected, and indicating markings in the
said that the whole affair was removed four or five
ground left by the tower from which it swung, he
The bricks were employed to aid in the
years ago.
the tube was bought by a Wandsworth broken, who
erection of an hotel visible a few hundred yards off;
cut it into sections, and sold them to a gentleman at
Wimbledon. These sections, with bottoms inverted,
formed tanks, from which the gentleman's cattle now
About the tramway there was some four tons
drink.
of wrought iron, which Mr. Stilwell himself had con-
formant could tell me nothing."
verted into horse-shoes. As to the object glass, my in-

his own

REPLIES TO QUERIES.

[2007]-TEMPERING DRILLS-If the drill is a small one hold it in a jet of gas till a cherry red heat appears, then dip the point, or as far up as you wish if a smooth file will bite or file it; if it does, it must be it tempered, into water or oil immediately. Then try done over again, but if it does not bite, but slips over the face without making any impression on it, it will do. Next clean the point or side of the face carefully on an oil stone, then twist a piece of wire round the end of the drill, or hold the end of the drill in pliers, or a candle or gas light till you see it (on the clean piece of the face) gradually turn from a light to a dark straw colour; withdraw from the heat, and allow it to cool gradually. If it goes past the dark straw colour to a blue it will be rather soft, and must be dipped in water or oil at once, or else the process gone over again. The above dark straw colour will bore brass beautifully. If it is to bore steel or iron, I have mine just as hard process, but care needs to be taken with them if very as when they come out of the water or oil in the first small in that condition, as they are very brittle. I have 14 years I have been working at my present profession. made several dozens in the above way during the last -A MORAYSHIRE MAN.

But

(2186.)-BAROMETER TUBES.-" Compensation" can clean his barometer tubes by washing with soap and warm water, and drying in an oven, or on a stove: or wash with spirits of wine, and it will dry itself when the spirit evaporates, or if the tube is very dirty, I have used fine sand with soap and warm water. scratch the inside of the tube, which causes more fricI do not approve of the sand, because it is apt to tion on the mercury rising in the tube, and consequently the barometer cannot be so correct. —A MoRAYSHIRE MAN.

[2363]-SILVERING CLOCK DIALS.-If "Poor Clock Jobber," 2363, page 68, carries the recipe given out further or fuller instructions, he will find his clock him by "J. M.. Birmingham," into execution, with

"Poor Clock Jobber's" dial, I shall be apt to say with
together), and rub woll on, and if this does not silver
the Editer (see p. 68). After it is well silvered, wash
in clean water (only). Dry with a soft towel; when dry
hold the back of dial close to a fire or on a stove till it
heats a little, not to be so hot as to melt the wax in
the chapters. Then varnish with a soft brush, varnish
to be made by dissolving gum mastic in spirits of wine;
"Poor Clock Job-
the varnish requires to be rather thin, and the article
will be ready in five minutes to be sent home. I have
no trouble with them afterwards.
done the above frequently with brass dials, and found
ber" may think I have been too long in answering the
above. But to explain, I get the MECHANIC only in
monthly parts at the beginning of each month, and
it, it comes 18 miles by rail ere I get possession of it,
when it leaves the bookseller's shop from whom I get
the carriage by rail of which I pay over and above the
[2445.]-GALVANIC BANDS.-The width of metal
regular price of publication.-A MORAYSHIRE MAN.

"the joints with thread
strips for galvanic bands is of no consequence; the
broader the more action. I have generally made them
List is the woolly selvage from cloth, for which ask
about in. wide. To "whip
is merely to wind thread round them in a close coil.
your tailor; it matters not which side is worn next the
touches it.-SUFFOLK AMATEUR.
skin, provided the bare metal at the end of the band

[2518.]-GAUGE FOR KITCHEN BOILER-My opinion is that if the boiler is properly fixed at the back of the kitchen range, the flow and return pipes For this properly erected from the boiler to the hot water cistern, a water gauge would be useless. drawn from the boiler but from the hot water cistern, through pipes connected to the return pipe. Consereason, when hot water is drawn for use, it is not quently when there is no hot water, it is a proof that the cistern is empty, and not the boiler, and a fitter is called in before any damage is done to the boiler.J. O.

[2528.]-MUSICAL. BOX.-From the poor way in which I expressed myself on p. 164, I may not quite be understood. The 16th and 17th lines should read. "The right end of the roller comee slightly over the edge of the same (that's the roller), and is caught in a slit," &c.-HARRY BERTRAM.

[2567.]-CHIMING CLOCK.-If "Toodles" will get them in the bottom of his clock case, lay a flat board found in the inside of couches, easy chairs. &c., lay on the top of them, or a bag of wood shavings, hay or three or four spiral springs something like what are straw, he will find that when the weight falls, coming in contact with the springs they will cause the weight to rebound, and so break the fall.-A MORAYSHIRE MAN.

[2577.]-BORING GLASS. This question relative to cutting circular holes in glass, does not appear to have been satisfactorily answered. As I, some time ago, required certain glass 'dises with holes in them, I went to Palmer's, in St. Martin's-lane, and I will, with your permission describe how their cutter procceded. There was, on a low table, a éircular disc of about a a pivot, so as to revolve on its centre, and there was a foot in diameter, covered with cloth, and mounted on mark to indicate this centre on the top of the disc. the top of the upright slid a graduated arm, and to the circumference of the disc. Through a hole near Then there was a firm upright fixed in the table near the end of the arm was affixed a glazier's diamond the disc. Now supposing I wanted a circular plate pencil which could be slid down so as to bear upon 6in. in diameter, with a hole in the middle of 2in. in the side was placed on the disc, the arm was diameter, A square of glass of rather more than 6in. from the centre, the disc was turned by the hand, and a circle of Gin, thus described on the glass; the arm now set at lin. from the centre and the inner adjusted so as to bring the diamond to bear at 3in. circle scratched. The glass was then removed and applied and a few cuts made with another diamond placed on the usual flat cutting board, a rule was from the outer circumference to the sides of the square. This enabled the workman to remove the superfluous glass from the outside of the circle. He then applied the rule again, and made 8 or 10 cuts

was

THE EAR "H. de S." says :-"Dr. Usher writes of having often been an hour in removing a plug of wax, and adds a caution against the cominon and indiscriminate use of the syringe. Will he allow me to inform him that glycerine dropped into the ear dissolves the cerumen, which is occasionally secreted in morbidly excessive quantity in the outer meatus of the ear in old people and in young children; and also that in certain forms of deafness, arising from a deficiency of the waxy secretion, it works often like good if fuller explained. If "Clock Jobber" will put about as many more. Then taking the glass in his

meatus, so as to

dial in about two or three months covered over with green spots, not because the recipe is a bad one.

It is

a charm when dropped into the
lubricate that passage and the external surface of the
membrana tympani? For this I am indebted to Dr.
Abbotts Smith's two little books on glycerine."
MIND AND BODY.-Edmund Lawrance says:quires more acid (owing to the acid not being pure) he
"Being deeply interested in the subject of Mind,' I
joyfully hail the appearance of Dr. Maudsley's lectures
in the ENGLISH MECHANIC. Man consists of two parts
only-soul and body Mind is the action of the soul.
The soul per se is not only ignorant and dark, but
totally unconscious of its own existence; as, during
perfect sleep, a faint, or upon concussion of the brain.
When, however, the nerve waves are set in motion,
the soul not only becomes conscious of existence and
recipient of present impressions, pleasurable or
painful, but it also finds it has the faculty of marshal-
ling and reviewing the impressions received and
registered by the nervous system during a whole life-
time. But the soul is utterly dependent upon the in-
If the images be dis-
tegrity of the brain register.
torted or misplaced by disease, the soul still accepts
those in simpie faith, and, attempting to reason upon
them, produces the well-known phenomena of in-
sanity."

COTTON SPINNING.-"B. H., Rochdale" writes: "I have read with interest the several letters on Cotton Spinning,' on page 182 and 183, and in reply to H. C. S.'' assertion that there is not, or ought not to be, any draught between the lap roller and feed rollers, he cannot have examined the question in a proper manner, or he would find that it is as needful in that part of the engine as any other, although it is very small-say, 1-in. With respect to the rule he gives for the draught of drawing rollers, he is perfectly right, as far as computing them together goes, and E. Slater will find that by his rule (if he gives the rollers the proportion he has set out, and then takes

1

10

across the inner circle, and crossed these again with left hand, and a pair of iron pliers in his right, he when nearly the whole fell out in fragments, and any began tapping lightly on the part that was cross cut, obstinate pieces were taken off with a grasp of the pliers. The whole process was gone through with great radidity, and was very dexterously done.

F. R. C. S.

[2582.-WEIGHT OF FRUSTUM.-TO Mr. TOLHAUSEN.

V =

H

3

× π (R2 + p2 + Rr) = 4 × 3,1416 (4+1 + 2 x 1) = 12·5661 x 7 = 8.79648 440 11 or - gives very nearly 17 2240 56 which, multiplied by put 10 for 7.-BERNARDIN. tons 27. By a simple error of copy our friend Mr. T.

a piece of silver in a tea cup, cover it over with nitric it does not, hold the cup over a jet of gas, or put it on acid (aquafortis), he will find the acid begin to boil. If a slow fire till it begins to boil. Take it off the fire, and it will boil away till the silver is dissolved. If he recan add a little, but the first quantity should do for dissolving a 6d. When dissolved, he will have a green deposit. Fill the cup with warm water, stir well to wash the silver, throw in gradually as much table salt as a penny piece will lift, desist stirring after the salt is put in, and allow the solution to settle a few minutes. The salt will precipitate the silver to the bottom of the cup. Pour off the water in the cup, care being taken not to pour off any of the solution, and when poured off as clean as can be without taking any of the solution with it, evaporate the remainder of the moisture above a jet of gas, or otherwise, till the solution is in a thickish kind of paste; when this is done, fill up the [2600.]-CLEANING OF DIATOMS.--Thanks to cup again with warm water, and repeat the process till the solution comes to a milky whiteness, and you I hope will give the desired result. In answer t Mr. A.'8 query as to where I gather Diatoms, I ma are sure all the nitric acid is out of the solution. Two Mr. Anderson for his kind reply on the above, whic or three washings is amply sufficient; if any trace of say that in spring they are to be found in almost an kind of water. There is a small brook near my hom the acid remain it will in time (notwithstanding the varnish) eat into the dial or other article, causing a "Poor Clock Jobber" will at once which I have hunted for a mile or two, and here an face of the silver. number of greens pots to appear, as it were, on the sursee the advisability of well washing his solution. The there where branches of trees and other obstruction browa yeasty seun, which betokens the presence parts to be silvered must be well cleaned with fine lie across the stream, so as to be only partly sub flour, emery sheet, or paper. No grease or dirt must merged, I have several times discovered the de touch the article, especially when finishing, not even the hands must touch it if possible. When well cleaned, Diatoms. The most successful gatherings I have y the article (I would not advise "Poor Clock Jobber" may be found also in ponds and ditches; if reed and all traces of previous silvering, or lacquering off made, were in ditches cut amongst osier beds. take a piece of wash leather or soft cotton rag, likely are they to contain Diatoms. I have found th to wash the article at this stage of the preceedings), rushes, &c., be growing in them, so much the mo soak it in water, dip it in a little salt. Rub the dial following:-Amongst the Naviculæ, N. Rhomboides, over with this first, pretty smartly. This makes the Amphisbona, N. Westii N. Didymi. Pleurosigma P. Attenu solution take ou better. Then dip the rag in cream of tra, P. Angulatum, P. Spencerii, Cacconema Lanceolatr tartar, and also in the solution (for they may be mixed | Pinunlaria viridis, Gomphonema Capitatum, Encyone.

The

[2667.)-PAINT TO COVER TARRED WOOD.All paint is affected when on a tarred surface, and the colour is generally turned to a green tint, a coating of lime, white wash, or two, would answer the end desired.-J. MEREDITH.

aespitosum, and several others, many of which I have| England in many respects: its winters are not so not yet identified to my satisfaction, as I am only a cold; its atmosphere is neither so foggy nor so damp; beginner in this interesting study.-BEATEN. but is uniformly genial, mild, and dry. The summers, [2634.]-PAPER HANGINGS.-As a continuation to although occasionally much higher in temperature A. Boughey's information (which applies only to what from the prevalence of north-west winds blowing is termed block printing) the question asked referring from the heated coast of Asia are scarcely so ener to machine printing, in machine work there are three vating or trying to the constitution from the bracing principal divisions, viz., pulps (plain), grounds nature of the sea breezes. Beyond this the purity and (coloured), and satins (both coloured and glazed). The freedom of the air from miasmatic influences and the first is printed plain-that is, without any preparation; usually noxious effects of night dews are such the second is coloured with either white or any tint that a person may sleep under the open canopy that may be required, and then printed; the third of heaven" at night during the greater part of is coloured and polished before it is printed. To the year without endangering his health or conmake grounds there is a grounding machine (of stitution. Regarding the colony of South Austhese there are several sorts); the colour is put on by tralia more particularly, I may say that generally it and smoothed with brushes, after which it runs the above description of climate is applicable through a long hot stove to dry, and at the end is to this part of the continent, although of course the formed either into folds or rolls, according to circum- proximity of mountains, rivers, arms of the sea, &c., stances; it is then ready for printing. Satins are will cause slight differences, according to locality. The made somewhat similar to grounds, only that they resources of this colony are chiefly mineral, yet agrihave to go through what is called the polishing culture and sheep-farming are pursued to an enormous machine to be glazed. The printing machine is cylin extent. The colony, however, may still be said to be drical, with revolving rollers pressed against it, on in an embryo state, and is capable of sustaining a popuwhose surface is placed or cut the pattern or form lation of probably not less than 50,000,000 of people, which each roller is intended to produce. When dried whilst at the present moment there are not more than the printed paper is taken to the rolling machines between 1 or 200,000 scattered over its enormous extent. and cut by young girls into pieces.-PRACTICAL P.S. The land is fertile, the yield of grain being large; of [2661.]-GALVANISING CASTIRON.-The method carefully cultivated, giving frequently 60 or 70bshl. to is essentially the same as for sheet iron, but there the acre. Its capabilities have been briefly summed is more difficulty in getting the zinc to adhere.-J. up by one of the governors as adapted to agriculture, MEREDITH. to pasturoage, and barren and unfit for either. tion about the colony. If it is too superficial, I am The above will give J. Francis some slight informaready to enter into detail, but wish as far as possible to condense this kind of writing, so long as the required information is imparted, so as not to occupy too much space. No one should emigrate to South Australia who is afraid of work. Do not go there with a firm intention to stick to your trade, for the probability is that you will find yourself before long following the calling of a shepherd. There is no shame in this, doctors and lawyers, &c., have tried their hands, and have succeeded admirably. The man who can handle tools, mend carts, repair farming imp lements, &c., is fortunate, he can command higher wages than his more unskilled fellow, even if employed upon a sheep-run, for being at a long distance from a large town, resources at hand are of great value. The best time of the year for sailing from England is during the autumn, as you will then arrive in Australia during the summer. I cannot state the best place for your ultimate destination; the demand for labour varying, as in all other places. Speaking of the neighbouring colony of Victoria, Mr Westgarth says:-"Hence a long array of miscellaneous arrivals, new and old, continuously out of work, while the skilled workman-the blacksmith, the carpenter, the stonemason-is but little beholden to employers, fights with them successfully at times over an eight hours' instead of ten hours' labour question at the same wages; and withal, in a country now on the whole cheaper to live in than England, earns as much in one day as many a home family must be content with for a week." This is a little exaggerated, for which allowance must be made. (Books consulted for information-"Guide to Australia, by a Merchant;" "Westgarth's Colony of Victoria;" "Maury's Physical Geography of the Sea;" "The Harrow School Atlas"-Essays.)-F.R.G.S.

[2676.]-MODEL STEAM ENGINE.-" C. R." was right when he said the model engine he saw had a cylinder, piston, fly-wheel, &c. Steam only acts on the piston during half a revolution of the fly-wheel, as will be seen by the following. A small block of metal is

fixed to the side of the cylinder at A, the face of which works steam-tight against the block B. The piston rod is fixed directly to the crank pin, so that when the engine is in motion the cylinder oscillates upon the pivot C. There are two holes in B, one the exhaust and the other the steamway. The hole in A serves for exhaust and steamway both. The action will be understood by examining the drawing.-W. H. THORPE, Reading.

[2679.]-HOW TO CURL AND CURE HORSE HAIR. In the first place I teased the hair well, then twined it into a long rope with a hand twiner with the assistance of another person, having rolled it up into a ball, steeped it in water 24 hours, after that put it into an oven, taking care that the oven be not too hot to singe it; after getting perfectly dried, I began to teaze it again, it is now ready for use, such as stuffing chairs, sofas, &c.-A HELPER OUT OF A Fix. [2683.]-IRON PALISADINGS.-The durability of ordinary paint or varnish would much depend upon whether the surface was free from rust or not. 1 would advise the use of Webster's patent zinc paint, which may be had from the patentee at Ozels-street, Birmingham.-J. MEREDITH.

[2693.]-KEEPING COPPER PLATES FLAT.Try reversing the plates.-T. S. U.

[2695.]-GEOGRAPHICAL QUERY.-" Key," as a correspondent, has said, is metimes the meaning of "quay," but also in several German languages" keizel, kei," has the meaning of flint or stoue. Let me propose then the translation nether set key"-a stone where burdens were set down, or, a stone for sitting on; key-house, a stone-built house: " key-spink "stone finch, stone sparrow, the doubtful sparrow, Fringilla petronia, Linn. Those acquainted with the locality will decide if I am right.-BERNARDIN.

[3703.]-PASTEBOARD.-Screw them up in a napkin press before they are quite dry for 12 hours; air them and repeat the process. 2nd, paste the edges of the first sheet of paper on a board or door; add as many sheets as you require for thickness, and cut off when quite dry. I have made equally good boards by both methods.-T. S. U.

[3706.]-PANCRATIC TUBE.-This may be illustrated on a small scale with any telescope. Unscrew the eyehole, draw out the small tube containing the two eyglasses as far out as it can conveniently be held by the fingers to be steady, and push in the focusing tube for distinct vision. An immediate increase of magnifying power will at once be evident. In all glasses with this appendage, the eye-tube mentioned above is contained within another, to which the thread of the eyehole screw is fixed, instead of to the outside polished brass tube. In Solomon's 3in. telescope, this tube reaches nearly to the field glass (the 4th from the eye), so that when fully drawn out, the length of the day eyepiece is doubled, and the sun and moon can be d'stinctly examined throughout the length of the tube, the magnifying power increasing according to its length. It is so long since I had them made, I forCan be get the price, but should say from 48. to 68. made by any optician. With a clear-sky and good light this tube is equally applicable to terrestrial objects. For this telescope, I find the Dean disc glass" for day powers, supplemented by one of deep blue for solar observation, answers perfectly, absorbing all the glare, and reducing the sun to the brightness of a white cloud. For a 2 in. telescope, I find a glass of "London smoke," one of deep and one of a lighter, blue required. Dean's disc " of "London smoke " may now be had from Messrs. Solomon' for 4s. 6d., the other glasses will be cut by any plumber for a 1d. each-AMATEUR.

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[3709.]-TURNING.-There is an error; the word "never" should not be there. It reverses the very meaning of the answer. It should read "An amateur will find a coarse, sharp, new file," &c.-Q. YORKE.

[3709.]-TURNING. See answer amongst the

Letters.

[3710]-ARITHMETICAL QUERY-If C c, represent the circumferences of any two different circles, and Dd their diameters, then Cc: D: d C: D:: c: d

[3598.] EMIGRANTS" INQUIRIES. - Upon reference to a map it will be seen that Australia is nearly at the same distance to the south of the Equator as England is to the north; in fact it lies very near our antipodes-that is, if by any means a line could be drawn directly through the centre of the earth from this country, Australia would lie near the point at which the line appeared upon the other side of the world. It may, under these circumstances, be at once inferred that Australia possesses a somewhat similar climate to our own. Climate is influenced by many local features, and to these we must assign the differences of temperature which exist between the or the circumference of a circle bears an invariable two countries. Australia, however, is superior to ratio to its diameter, and of course to its radius.

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Now this number is the same for every circle, and it is obvious that a single accurate measurement should be sufficient to determine it. It might appear at first sight that nothing can be more easy than to take a perfectly constructed circle and measure its circumference with a cord: and then measure the diameter in like manner, and find the ratio of two measurements, which will give the numerical value of But it is found that the ratio of the circumference of a circle to its diameter cannot be exactly expressed in numbers. Each se parately can be measured with perfect exactness, but both do not admit of being measured exactly by the same linear unit, however small that unit may be. Practically - or 3-is found to express for many purposes with sufficient exactness the value of is still nearer, but

355

113

22

7

1

7

31416 or 314159 is in general use. Now, suppose we have a regular polygon with a perimeter of 8 and number of sides 4. Then 1 is the rad. of inscribed circle, and 1-414213 is found to be the radius of circumscribed circle. Also if we have a regular polygon of 4096 sides with the same perimeter, the rad. of inscribed circle is 1-273239, and that of the circumscribed circle is the same. Thus the circumference of either circle will not differ from the perimeter of the polygon between them by a quantity so great as 00001 because the radii do not. So that we may conclude that the circle whose circumference is 8 has a radius equal to But

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diam.

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(diameter) x 7854. Now the circumscribed square is The arca of a circle is found by the formula equal to the square of one of its sides, which is equal

to the diameter of the circle. Therefore we must

multiply areas of squares by the decimal 7854 to get areas of circles; and not areas of circles to get area of squares.-J. G. G.

[3717-COPPER AND SILVER COINS-The first is a French coin of Duke of Rohan; the second an Arabian.-COLLECTOR.

[3718.]-TALL CHIMNEYS.-The great chimney at St. Rollox, Glasgow :

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There are used in its construction 1,250,000 bricks of first quality, weighing 1211b. per cub. ft., the brickwork is 34 bricks at the bottom, and 1 at top. The peculiar construction is that of a double cone, the internal fiue is 260ft. high, and is perfectly vertical.E. N.

[3721]-GRINDING.-In answering the inquiry of "Sergius," I should say that 4 bush. per hour, more or less, was a fair average for a 4ft. stone running 120 revolutions per minute; but 200 revolutions for a pair of 3ft. 4in. seems to me too fast. Templeton gives 150 as speed for 40in, stone,dividing 6 00 by the diameter in inches; but it is a bone of contention with millers as to how much a stone ought to do, even with plenty of power; some not liking to do more than 3 bush., others will advocate 5, much depending on the stone ard the dryness of wheat: and I should not be surprised if my letter gives rise to more controversy than the balancing business, of which so much difference of opinion exists-solely, I believe, because a stone that is in standing balance is generally in running balance, or so near to it as not to be felt when there is a moderate amount of feed under; and I believe there are millers who would boast a life of experience without simply because they never run them empty to try. I knowing their stones were out of a running balance, well. I have also a pair of 4ft. Gin. which will do 10 have 2 pairs of 3ft. 10in. which will do 4 bush. per hour bush. per hour well, and work well, but they have 5 in. draft. These said 4ft. 6in. had formerly 2in. draft, and I understand they would only do 4 bush. per hour; the the master furrow; thus making a second furrow of alteration was made by running all the furrows into the master furrow. There is a pair of 4ft. 4in. laying beside them, both driven by wind, running the same speed; but they will not do so much by about 3 bush. per hour, although they had the same alteration made in the draft and furrows at about the same time-say 40 years ago. Now I have seen these two pairs of stones do nearly a load of wheat in 2 hours. We find no disadvantage from the extreme draft, but dare not carry much furrow.-ONE EYE.

[3723.]-GLAZE FOR POTTERY.-100 parts white! lead, 20 do. flint, 40 do. flint, 5 do. whiting. This glaze is colourless; to make it a brown glazo add 18 parts of oxide of manganese and 18 parts more white lead; to make a blue glaze, substitute for manganese 9 parts of oxide of cobalt. Shall be happy to afford "X. N." any information he may require upon this subject.-R.

[3723.]-GLAZE FOR POTTERY.-Consult specification of Patent 357, 30th October, 1867, at your

nearest public free library, which I think may give the information you require.-A. TOLHAUSEN.

TOLHAUSEN.

and stirred; not the head this time, but a lid is put on. It is now left for two hours in brisk ebullition, [3725.]-VULCANISING RUBBER. The rubber then strained and expressed as before. A boiling ready mixed with sulphur for vulcanising, may be obsolution of subacetate of lead (acetate of lead 5 parts, tained from C. Macintosh and Co., Cambridge-street, itharge 3 parts, distilled water 16 to 20 parts, Manchester, and London, or David Moseley, Manchester boiled for half an hour) is poured in just as it is The price will depend on the proportion of sulphur. (without filtering) till it ceases to occasion any prerequired, which varies for each special purpose, per- cipitate. I allowed it to stand all night to settle. haps 2s. 6d. or 3s. per lb., in quantities. The moulds Early on the following morning I drew off with a should be pure tin or plaster of Paris. Iron combines syphon as much of the clear supernatant fluid as I could; with the sulphur, and destroys the nature of the rub- the precipitate I submit to pressure. I avoided the ber. Any steam tight chamber may be used for vul- disagreeable process of sulphuretted hydrogen by canising in (which will stand the pressure) Informa- the substitution of oxalic acid. The excess of lead tion respecting the time required, and the pressure, was then thrown down as an insoluble oxalide. I may be obtained from the persons who supply the rub. added a little ammonia to take up the free acid, drew ber, or you might try a pressure of 50 or 55ĺb. on the off the clear liquid, boiled it down to 2pts. or so, in. for 3 or 4 hours. When you get it exactly as you poured it into a gal. bottle, then allowed it to get want it, adhere strictly to the same time and pressure, cold (what beautiful crystals fill the liquid as it cools!); as the slightest variation alters the nature of the when cold I added about 4 fluid oz. of chloroform to rabber.-A DENTIST. the contents of the bottle, and after briskly agi(3725.]-OILED PAPER.-Hausel, of Neustadt, re-tating them for 5 or 6 minutes I let them settle; the commends petroleum applied to writing or drawing chloroform quickly fell to the bottom colourless and clear, whilst every crystal had vanished out of the paper, and properly dried by blotting paper. A liquid. The chloroformic solution of theine was then taken up by a glass tube, drawn out to a capillary [3730.]-PAPER COLLARS AND CUFFS.-A neat point, and discharged into a flask. The chloroform machine for the manufacture of collars, cuffs, and other was then distilled off by a water bath into a Liebig's articles of dress made of paper and cloth combined, condenser, and on detaching the flask from the conwas patented by Mr. Benjamin Browne, in 1868. The denser I found the theine left dry and white. It gave material is first operated upon to represent stitching, me entire satisfaction in the shape of a good sample creased for folding, the button holes punched, and the of theine. I should be pleased to be equally sucends cut off to the desired shape; the article is then cessful with digitaline. Surely one of my brother discharged from the machine, and another feed of readers has attempted digitaline with as happy a paper supplied and operated upon as before, and so result as mine as regards to theine. If there is such on in succession. Finally the article is passed by an a one among our many, may I beg of him to explain endless belt between rollers for finishing it (vide the way he proceeded?-PHARMACEUTICAL STUDENT. specification, A.D., 1868, 16th March, No. 1040).-A. TOLHAUSEN. [3763]-CAFFEINE OR THEINE.-The general [3733]-COTTON SPINNING.-J. A. Hulsse, “Die method adopted in the preparation from tea or coffee Tichnik der Baumwollspinnerei," Stuttgart and Augs- infusion with subaretate of lead to precipitate the is by pouring on these boiling water, and mixing the burg, 1857; J. D. Fischer, "Dir praktische Baumwoll- tannin. Piligot adds subacetate of lead in excess, spinner," Leipzig, 1855; C. H. Schmidt. "Lehrbuch then am monia. The mixture is boiled for some time, der Spinnereimechanik," Leipzig, 1857: K. Karmarsch, the lead-precipitate carefully washed on a filter with "Handbuch der mech. Technologie," Hannover, 1858 boiling water, the filtrate freed from excess of lead Bd. S. 1006-1103-Supplement zu Prechtl's Tichnolo by sulphuretted hydrogen, and after a second filtragischer Encyclopadie, (Karmsrsch), Stuttgart, 1857. The above books may be had in London. Trubuertion, evaporated at a gentle heat. On cooling, it yields an abundant crystallisation of nearly pure theine, and and Co., Paternoster-row. Benno Niess, "Die Bauman additional quantity may be obtained by concen wollen Spinnerei in all ihren Theilen " Voigt in Weimar; Dr. E. Hartzig in Dresden Versuche uber rating the mother liquid, and leaving it to crystallise. den Kraftbedarf der Maschinen in der Flachs und limation, gradually heating waste useless tea in a Caffeine being volatile, it may also be prepared by subWergspinnerei; Schweiz. Polyt. Zutschrift Vol. sublimation apparatus. Part of the sublimate is quite XIV., Heft 5. Sute 126.-A. TOLHAUSEN. pure; the rest may be purified by recrystallisation from water. For further details ride" Watts's Dict of Chemistry," from which the above has been extracted. A. TOLHAUSEN.

** [3739.]-CHLORIDE OF TIN.-Three chlorides of tin are known, corresponding to the oxides, namely SuCl2, SnC16, and SnCl4. See Watts's "Dict. of Chem.," vol 5, page 806.-A. SOLHAUSEN.

[3768].-POISONING BY CANTHARIDES.-The effects of cantharides are only transient, and the results attributed to it by the querist can only exist in his imagination.-M. D.

[3778.] LIGHTHOUSES.-The querist will find in "Merveille's de la Science, par L. Figuier" all the can be had separately; lighthouses occupy, I believe, 5 or 6 numbers.-BERNARDIN.

[3739.1-CHLORIDE OF TIN.-If this querist will 2sk at a manufacturing chemist's for protochloride of tin, he will most likely get what he requires.-A. T. [3741]-TURBINE-In answer to "M.R.C.S.," if he will write to me I will try to assist him to see a turbine, as there are three in my neighbourhood.-particulars he may desire; every number of that work JOHN WILD, Shuttleworth, near Bury, Lancashire. [3750.]—SILVER COIN-Is a penny of Baldred, King of Kent (the last). Obv.: King's bust to right; Baldred Rex. Rev Moneyer's name Edelmod Moneta, small cross, 7 rays issuing (scarce). Should be glad to communicate with "Beginner."-J. H. D., Stretton-on-Dunsmore, Rugby.

[3782.]-BOILER-I do not know much about small boilers, further than their requiring much bigger fireboxes, in proportion, than large ones, on account of the difficulty of keeping a small fire alight. For such a boiler as "Hydraulican" figures, possibly a well ar[3751. ASCARIDES. — A great sufferer from ranged gas fire would do. I should, for a coal fire, put ascarides should take 20 drops of tincture of iron in about 14in. square of fire bars, then slope the walls of infusion of quassia twice or three times a day for a fire-box outwards at about 30% away from the perpenmonth, and use an injection of common salt dissolved dicular for, say, 8in., and then contract the walls again in water, but not made too strong, occasionally. This at about 45°, till your pot will just fit on. It is of an generally succeeds, but cases differ, and no case can awkward shape to make a fluo round to water level, be satisfactorily treated by correspondence. Any and I should say seven 2 tubes would be better than chemist can make up the above prescription.-M.D. one. The brick work might be gradually altered from [3753.]-BOTANY.-A “Manual of Botany," by Robert square at bottom to round at top; and the reason for Bentley, Professor to the Pharmaceutical Society, pub-radiating heat, besides what is conveyed up the tubes. the form I suggest, is to get a great surface for lished by Mr. Churchill, 128. Gd., is the standard work upon which the students are examined, and is deci- fire bars, even if it has to be made moveable for raking I should put the dead plate on a higher level than the dedly the best.-F. H. H. will, perhaps, give you a hint. I was very successful out the fire. Somebody who knows better than I. with a cylinder boiler only 4ft. long, by 2ft. diameter, which drove an engine 4 diameter, and 8" stroke, for months, and the man in charge said he always had steam, and the fire-door generally open: of course only doing light work.-J. K. P.

[3753.] BOTANY. - Use Babington's "Manual of British Botany," or a similar work by Johns. The latter is more popular, and easier to work with, and costs about 78. I believe.-M. D.

[3762]-PAINTING AND DECORATION.-The best work on house decoration and painting that I have seen, is by William Sutherland, Manchester; obtainable from Simpkin, Marshall, and Co., Stationers' Hall-court; Abel Heywood and Son, 56 and 58, Oldham-street, Manchester.-PAINTER.

[3763.]-THEINE. I perfectly succeeded in the isolation of theine by operating on 21b. of the best green tea as follows:-2gal. of distilled water, where brought to the boiling point in a still of 4gal. capacity; I now shoot in the tea, stir up for an instant, quickly lute the head on, connect it to a worm condenser, and ebullition commences. By the above arrangement of apparatus you will observe I was able to collect, previous to the isolation of the theine, another highly important compound of tea-viz., the essential oil. Note also, by having the water at a boil I avoided the risk of charring the leaves, which doubtless would have occurred if the still had been placed over the fire with cold water along with the tea. I kept it gently boiling for two hours. About 14pt. of water passed over loaded with the oil. On agitating this water with ether, decanting and evaporating the ether, I obtained the oil in a separate form. This oil appeared to me to be a powerful intoxicant, for on my warming it and applying my nose, it had an effect similar to smelling hydrocyanic acid of high per centage. I now set to work for the theine emptying suspended from spikes on a frame furnished with four legs, allowing the filtrate to run into a large tin vessel. I now pour 2gal. more of distilled water into the still, which I place over the fire; I collect the leaves off the strainer into a dish, and submit them by portions to powerful pressure in a tincture press, allowing the expressed liquid to flow on to the strainer. The hard cakes of leaves from the press I knock and break into pieces, crumbling them into a loose heap The water in the still is now boiling, the leaves are shot in again

the contents of the still on to a brown calico strainer

[3794.]-POLISHING STEEL-TO"CYLINDER." Use your "red stuff" on a bell metal polisher, which can be had at any watchmaker's tool shop, and you will get the black polish you so much admire. The scratches are caused by dust getting into the polishing stuff. The pivot "Cylinder" has marked A is a straight pivot, with the shoulder turned away after it is made. B is a cone pivot, which is proper for a balance staff. The other is only an attempt. A cone pivot is made by first turning down nearly to size, and then polished with a polisher, the shape made of a stick of straight steel wire. That part held in the hand should be draw-filed. to prevent slipping in the fingers, and the other end filed the shape of a crossing file, to suit any shape, and give it a slight rotary motion backwards and forwards, as well as the longitudinal motion. This will prevent rings forming. When finished, turn a groove close to the pivot, to prevent the oil running up the staff, away from the pivot.-VIATOR.-P.S.-There are several other watchmaking questions asked this week; but the subject only interests the individuals. I never yet heard of an amateur watchmaker.

[3804.]-WATCH CLEANING.-J. D. Morgan will require for watch cleaning, a pair of tweezers, plyers, cutters, a screw-driver, and a brush. I myself (an amateur; got my tools and part information from the Watch Tool Warehouse, (S. Fauenberg's, of Leeds); but perfection will come by practice.-N. T.

[3817.)-STEAMING WOOD.-The apparatus for steaming wood consists of a wooden chest, large enough to contain the work. This is connected with a covered boiler or copper, in which the steam is generated. "W. B." does not state for what purpose he requires the stuff steamed, or the size of the same, so that his query cannot be answered satisfactorily. Large stuff requires

more steam than thin stuff. An inch oak board will take about twenty minutes, and sets in two or three hours. In forming moulds for the hot timber to be shaped to, care should be taken to give a sharper curve than wanted, to allow for a slight reaction.-BOAT BUILDER.

[3821]-WHEEL CUTTING.-In reply to J. K., England, the teeth I cut were not wheel teeth, but floats similar to cabinet-floats, about 10in. and 12in. long, for roughing the metal off the tubes that gun barrels are made of. The side view of them shows them to be like pit-saw-teeth, and skewed on the plane. I merely wished to point out that the difficulty of having change wheel of steel did not lie so much in the expense of merely cutting the teeth, as in obtaining the stuff to make large wheels of.-J. K. P.

face of the instrument like the iron of a skew rebate

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[3822.]-FORCE PUMP.-It seems to me that Guernsey Amateur" is sufficiently exigeant in wanting a drawing first made exactly to his requirements, and then to expect the Editor of the ENGLISH MECHANIC to go to the expense of having it cut and printed; particularly as he does not seem apt a he can give a description of the action of a chuck that making an ordinary working drawing out. And yet ing the vial of my wrath on him for the abuse I have I hope he will not think I am pour

hehas never seen.

received from an amateur in another of the Channel boiler is to have a hand pump that will throw at least Islands. I think the best way of supplying a small half a cubic inch of water at a stroke; and to supply the boiler that way, where you see by the water gauge that it wants it. Small pumps are extremely troublestop the engine directly the pump ceases to act-viz., some; at least, I have found them so, as you have to about once every half minute or so. You can put a dummy, for the sake of appearance, to your model.— J. K. P.

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of amateurs not understanding a drawing, even
[3823]-SLOT CUTTING.-Here is another instance
put in a drill chuck or else in a driller like mine,
with a description. The tool figured was meant to be
figured Nov. 12th, last year, and either it or the work
travelled backwards and forwards between two stops
to regulate length of slot, and fed inwards for metal
about--in. or less during each trip. 1" in 5 minutes
is not bad work for a drill to do, but I do not think
speed.
the twist form of tool would keep on long at that
Mine was meant for wood, and shown with
edges too keen for ordinary metal. I cannot give any
time to this subject just now.-J. K. P.

103

does not say whether he wants a drawing of the whole [3833.]-FROM “BOAT BUILDER.”—J. F. O'Brien canoe, or any particular parts. If the former, at lin. to the foot scale, it would be too large for our MECHANIC, but if he will publish his address I will post it to him.

-BOAT BUILDER.

(3835.]-CLEANING COINS.-I find the following effectually clean old coins so as to read the inscription. First lay them in vinegar, and then rub thei with silversand and water-Toм C. HOLLOWAY. [3835.]-CLEANING COINS.-J. Nash will spoil his coins if he cleans them. To decipher an obscure inscription take a cast of the coin with wax, and a copy of that impression with plaster of Paris. will show the letters much more clearly than the coin. When a coin or medal is completely worn smooth, if they are heated red hot, say on an iron bar, the original inscription will be generally quite easy to read, although the metal of the coin itself is quite flat.-Q.

YORKE.

NOTES AND QUERIES.

This

Would any

[3838.]-PRINTERS FURNITURE. reader inform me what plane they use in making printers' furniture, especially reglets, and how they are held while planing them?—A CARPENTER, [3839.]-TRACING CLOTH.-Can any reader inform me of a means of colouring on tracing cloth (such as used by engineers and architects), without injuring the cloth? Also, if there is any substance I could mix with the Indian ink, so as to make the cloth take on the ink more readily ?-TRACING.

[3840.]-MUSHET'S STEEL.-Will any reader inform me, through the medium of your valuable paper, how to manage Mushet's special steel, and what shape is the best for roughing tools; a small sketch will oblige. I have tried it many times, and I find it too soft?-J. M.

kind reader inform me of a cheap and easy method of [3841] GRINDING DRUG SEEDS.-Will any grinding drug seeds, fenugreek, &c., on a small scale?

-F. H. H.

[3842.]-STEEL WIRE.-Would the "Harmonious Blacksmith " kindly inform a musical mechanic, where to get some steel wire of different gauges, such as is used for gongs in American clocks, or the gongs ready made would suit as well? The querist wishes to make a set of chimes, to be put in a model church, and bells are too dear?-J. R. Y.

[3843-FLY ROD.-Would "Vivis Sperandum kindly say how he fitted the end joints on his fly rod, and also where to get wood and all other materials suitable for same, as I have long been wishing to make one. I hope this will not pass his notice, as 1 think it will interest more than one of us.-REGULAR SUBSCRIBER.

[3844]-ENTOMOLOGICAL QUERY.-I would feel much obliged to any of your entomological readers, who would describe the larva of Cosmia trapezina; it is said to eat its neighbours if placed in the same box with them, which I would avoid if I knew it?-E. N.

[3815.]-BOEHM FLUTE-Can any fellow reader explain the mechanism of the Boehm flute, also what are the ring holes on clarionets ?-ANOTHER FLAUTIST.

[3846.]-NICKEL, OR GERMAN SILVER-Can a y reader tell me what is the composition of German

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